Intriguing.

I contacted Microchem who put me in touch with Chestech (Uk supplier).
Andrew Cooper of Chestech sent me the following email about this
subject. I'm pretty sure he will have no issues with me divulging what
he said on this forum.

"Hi James,

I've been sent your request Via the MCC server.

SU-8 & KMPR do indeed have superior etch selectivity over Novalac
resists. SU-8 & KMPR are both chemically amplified resists and without
PEB the 2nd phase reaction will not take place, and the resist will not
cross-link correctly meaning poor image quality if it images at all.

I think he's talking about elimination of Hard-Bake and not PEB that
would make more sense, with no Hard-Bake the resist might be easier to
strip but still difficult compared to Novalak."

Both Bob Henderson and Brubaker Chad however contradict Andrew's
comments above.


Brubaker Chad wrote:
> This could definitely work, especially depending on the time between exposure
and develop. As soon as the SU-8 is exposed, it begins crosslinking, but at room
temperature, this crosslinking occurs slowly. Its possible that enough crosslink
occurred to allow development with reasonable fidelity, without crosslinking
beyond the point of ashability.
>
> I've done processes similar to this myself.  Based on my observations, SU-8
crosslinking is a catalyzed process - once the photo-acid is present (in any
quantity), it will begin the cross-link process.  Concentration of acid
(controlled by exposure dose) influences rate of reaction, as does temperature
(as in most chemical reactions, heat accelerates the process).
>
> By reducing the concentration of the acid (reduced exposure), and reducing
reaction kinetics (lower temp bake), I've been able to crosslink SU-8
sufficiently to pattern it (at >100 µm thick, and maintaining near 90º
sidewalls), while still being able to bond the material via standard
thermocompression bonding (which requires some degree of reflow in the SU-8).
>
> Best Regards,
>
> Chad Brubaker
>
> EV Group
> invent * innovate * implement
> Senior Process Technology Engineer - Direct: +1 (480) 305 2414, Main: +1 (480)
305 2400 Fax: +1 (480) 305 2401
> Cell: +1 (602) 321 6071
> E-Mail: C.Brubaker@EVGroup.com, Web: www.EVGroup.com
>
> -----Original Message-----
> From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On
Behalf Of Bob Henderson
> Sent: Tuesday, September 15, 2009 1:23 PM
> To: 'General MEMS discussion'
> Subject: Re: [mems-talk] SU8
>
> James:
>
> This has been a long time ago but if I remember right we treated it just
> like negative working resist. That is we had a special SU8 that would
> produce a 5 micron film at 3,000 rpm spin speed. After coat we did a soft
> bake at 70 degrees C for 30 minutes in a Blue M oven. Then we exposed on a
> contact aligner to cross-link the exposed areas with proper wavelength of
> light. Then we developed using Xylene followed by N-Butyl Acetate for a
> rinse. The sidewall profile was 90 degrees and it had much better
> selectivity to a silicon etch than any positive resist we tried. That is all
> I remember but you can contact MicroChem as I am sure they have advanced
> the formulations since then.
>
> Bob Henderson

--
Dr. James Paul Grant
Postdoctoral Research Associate
Microsystems Technology Group
76 Oakfield Avenue Room 3
University of Glasgow
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Scotland
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